Weather Data

Advanced Infiltration with AIM-2Red Calc Tool User Guide

What this tool can do for you

This tool calculates the hourly infiltration for a selected date range
(one day to one year) and the resulting sensible load on a heating
and/or cooling system. Daily average infiltration rates (stack, wind,
and combined) and daily infiltration load on heating and cooling systems
are displayed on separate charts for the selected date range. Additionally,
balanced or unbalanced ventilation can be combined with infiltration with
the results displayed in a table and on a chart, along with the resulting
additional load on the heating and/or cooling system. The tool
combines the powerful AIM-2 infiltration model with typical
meteorological year data (TMY3 for the US and CWEC for Canada) for over one thousand weather locations
in North America. The tool can be used for:

Tips

Clicking the label for any input or result will cause a
popup help box to appear. This help box includes the
allowed and normal values (for inputs).
Read more.

This tool, based on the AIM-2 infiltration method, is not intended for
buildings of more than three stories above grade, or for multi-unit
buildings.

All the results under the date range selectors are calculated for
the date range you select.

The low (high) values in the table will most likely be lower (higher)
than the lows (highs) in the first chart. This is because the chart
plots daily average values, while the table reports
hourly values.

Use the default percentages for leakage distribution unless you have
reason to believe you have more accurate vales. The default percentages
are dependent on the building height and whether or not the building
has a vented crawlspace.

Make sure you read the pop-up help for "Terrain category" and "Building
shelter class" before making your selection from the drop-downs. Click/touch
on the input label to read the pop-up help.

Regarding the "Building has open flue/chimney" section inputs:

Do not include flues and/or chimneys that are closed, such as
fireplaces with tight-fitting dampers.

If there are multiple open flues, add their areas and average
their heights.

Interactive chart use

This tool includes three interactive charts that can be used to display
results; it may also be used for educational, sales,
and marketing purposes. For example, you can save a chart in one of four different
file formats, embed it into a customer report, or print it separately.

Tips for using the interactive charts:

Click/touch the series labels in the legend of either chart to
turn the corresponding chart data on or off. For example,
in the first chart, you can turn on or off the data series for
"Stack", "Wind", and/or "Total".

Click/touch the menu icon in the upper right corner of the chart
to show the choices for printing the chart or downloading it as an
image file in PNG, JPEG, PDF, or SVG format. You are free to use the
downloaded image in any way, including reports,
presentations, websites, as long as the attribution for
"Residential Energy Dynamics, LLC" is included.

If you save the chart as an SVG file, you can change the
title or any other chart element with the use of third-party
software. Examples of third-party software include Inkscape
(a free version is available) and Adobe Illustrator.

Inputs and field measurements

Closest weather station - select closest station from three drop downs.

Building leakage @ 50Pa - value from standard blower door test at 50
pascals. Ideally, this should be corrected to standard conditions
at seal level. This can be done using either the ASHRAE 6.2-2010 or
ASHRAE 62.2-2013 ventilation tools.

Pressure exponent - use default of 0.65 unless you know the value for the
building in question from a multipoint blower door test.

Building height - the average distance between (a) the bottom
pressure boundary, or grade, whichever is higher, and (b) the top
pressure boundary. Generally one story is 8.2 feet (2.5 meters),
two stories is 16.4 feet (5 meters), etc. The enclosed volume
should correspond to the door positions used during the blower
door test as much as possible.

Building has a vented crawlspace - check box for indicating that
the building sits on top of a vented (or open) crawlspace. This
affects the default leakage distribution and the wind infiltration
calculation.

Building shelter class - five possible selections from a drop down.

Terrain category - four possible selections from a drop down.

Thermostat setting, (heating) - if a daily setback is used,
estimate the average indoor temperature during the heating season.

Temperature credit for solar & internal gains (heating) - the number
of degrees, on average, that solar and internal gains increase building
temperature during the heating season. This input should not include
the influence of mechanical ventilation.

Thermostat setting, (cooling) - if a daily setback is used,
estimate the average indoor temperature during the cooling season.

Temperature penalty for solar & internal gains (cooling) - the number
of degrees, on average, that solar and internal gains increase building
temperature during the cooling season. This input should not include
the influence of mechanical ventilation.

Height flue extends above grade - if the grade is uneven, use an
average. The default value is the building height plus six feet.

Flue cross-section type - three possible selections from a
drop down.

Flue dimensions - inputs for diameter and rectangular shapes.

Building has ventilation system (optional inputs): Check if building
has a whole-building ventilation system as defined by ASHRAE Standard
62.2.

Balanced ventilation rate - A heat recovery (HRV) or energy
recovery ventilation (ERV) system or balanced supply and exhaust
fans. If there are supply and exhaust, but they are not completely
balanced, enter the portion that is balanced. The remainder should
be entered in the "Unbalanced ventilation rate" input.

Sensible recovery efficiency (SRE) % - A measurement, that does not
include latent heat recovery, used in determining the amount of energy
passed between airstreams in a heat or energy recovery ventilator.
This value is provided by the manufacturer of the HRV or ERV.

Unbalanced ventilation rate - Flow rate from an exhaust-only or
supply-only fan, or the unbalanced portion of a combined exhaust-and-supply
system (HRV, ERV, or combined exhaust and supply fans operating
simultaneously).

Method for combining with infiltration - Unbalanced ventilation changes the house pressure,
which interferes with natural
infiltration so that we can not simply add the two rates together. The reality is that
unbalanced ventilation and infiltration combine in a rather complicated way. There are two
competing approximate methods in use for combining ventilation and infiltration.

Quadrature - This is the method specified in the ASHRAE Handbook of Fundamentals and is our default
method. For quadrature, the combination is given by
BalVent+UnbalVent2+Infil2

0.5 Rule - This method is preferred by many practitioners. It may give better results
in some situations in which the natural infiltration is dominated by the stack effect.
For the 0.5 rule, the combination is given by
BalVent+max&ApplyFunction;UnbalVentInfil+0.5×UnbalVent

Background

The Alberta Infiltration Model (AIM-2) applies to low-rise (up to three stories)
detached, single-family, residential structures. The development of the
empirical model began in the 1980s and was more finely developed over the next
decade by David Wilson, Iain Walker, Larry Palmiter, Tami Bond, Max Sherman,
and others.

For the mathematical model used for this RED Calc Free tool,
"over 3400 hours of measured ventilation rates from the test houses at the
Alberta Home Heating Research Facility were used to validate the predictions
of infiltration rates and to compare the AIM-2 predictions to those of other
infiltration models. The AIM-2 model had bias and scatter errors of less than
15% for wind-dominated ventilation, and less than 7% for buoyancy ("stack-effect")
dominated cases." [Please see Walker and Wilson in "References" section below.]

Best practices

Select the weather station closest to the site you are analyzing. If your
location is close to a state border, you might find the closest weather
station is in another state. The map feature in the
Weather Station Data (TMY)
tool is helpful for determining this.

References

ASHRAE. 2013 ASHRAE Handbook: Fundamentals. Chapter 16, Ventilation
and Infiltration, page 16.24. Atlanta, GA: American Society of Heating, Refrigerating and
Air-Conditioning Engineers, Inc. This document
may be purchased at www.ashrae.org.
Comment: Here the AIM-2 infiltration model is referred
to as the "Enhanced model". Also, equation (51) on page 16.25 shows
how ventilation and infiltration are combined.

Walker, Iain and Wilson, David. Field Validation of Algebraic Equations for Stack and Wind Driven
Air Infiltration Calculations LBNL 42361. 1998. Lawrence Berkeley National Laboratory.
http://epb.lbl.gov/publications/pdf/lbnl-42361.pdf
Comment: This is the paper that explains the AIM-2
infiltration model. From the abstract: "Over 3400 hours of measured
ventilation rates from the test houses at the Alberta Home Heating
Research Facility were used to validate the predictions of ventilation
rates and to compare the AIM-2 predictions to those of other ventilation
models. The AIM-2 model had bias and scatter errors of less than
15% for wind-dominated ventilation, and less than 7% for buoyancy ("stack-effect")
dominated cases."

Related tools

Design Infiltration with AIM-2:
This tool calculates the stack-induced, the wind-induced , and the
combined infiltration for given indoor/outdoor
temperatures and wind speed. The primary use case is determining
the design infiltration rate that can be used in a
heating or cooling load calculation for system sizing.

Weather Station Data (TMY):
The embedded Google map feature helps you find the closest
(TMY) weather station when your location is close to a state/province or
national border and the closest station is actually in a different
state/province/country. Additionally, the tool's interactive table and chart help you explore the
the Typical Meteorological Year (TMY) data for each of 1,100 weather
stations in North America. This hourly data is the foundation for
most building energy simulation software.

ASHRAE 62.2-2013 Ventilation:
Determine whole-building ventilation requirements for new and existing
dwellings, with the choice of using advanced blower door options and
the alternative compliance path.
Comment: Use the "Use Advanced Blower Door Inputs" of
this related tool for a more accurate "Building leakage @ 50Pa" input.

ASHRAE 62.2-2010 Ventilation:
Determine whole-building ventilation requirements for new and existing
dwellings, with the choice of using advanced blower door options and
the alternative compliance path.
Comment: Use the "Use Advanced Blower Door Inputs" of
this related tool for a more accurate "Building leakage @ 50Pa" input.

Related external resources

The Energy Conservatory. SeeStack Training Simulator software tool.
http://www.energyconservatory.com/software
Comment: SeeStack is a free graphic training tool that allows the
user to experiment with different variables of a house, including the number of floors,
type of ventilation, different indoor and outdoor temperatures, and
more to visualize stack effect. It includes some of the same variables
that the RED Calc Advanced Infiltration tool
does and enhances one's understanding of infiltration, neutral pressure planes,
and the interreaction of infiltration and ventilation. This tool runs
on PC computers only.